CRUSTAL MOVEMENTS 201 



vibrations which we can feel; but they are sufficient in some cases 

 to produce great earthquakes. 



Surface changes caused by earthquakes. The changes in the 

 surface of the land made by earthquakes are numerous if not im- 

 portant. Besides the cracks and fissures, and the risings and 

 sinkings of surface, which have been noted, drainage is often dis- 

 turbed. This is partly because of the cracks and fissures which are 

 opened, and partly for other reasons. If a fissure is opened across 

 the course of a stream, the stream \vill plunge into it. Springs are 

 often disturbed, old ones ceasing to flow and new ones appearing. 

 This is probably because the earthquake movement has broken the 

 rock beneath the surface, and so changed the course of the ground- 

 water circulation. Temporary spouting springs are sometimes 

 formed, water being forced up violently through them. This was 

 the case in the Charleston earthquake. Earthquakes sometimes 

 cause landslides, and if the material from a mountain-side slides 

 down, it may dam the valley below so as to disturb its drainage. 



From fissures and from lesser vents noxious gases sometimes 

 issue. 



Earthquake waves have a singularly destructive effect upon 

 animals which live in the water. In many cases, animals of rivers, 

 bays, and even of the ocean have been killed in extraordinary 

 numbers during an earthquake. 



REFERENCES 



1. Standard text-books on Geology, under Changes of Level, Secular 

 Changes of Level, Crustal Movements, Earthquakes, etc. 



2. SHALER, Chapter on Earthquakes in Aspects of the Earth: Scribners. 



3. GILBERT, Pop. Sci. Mo., Vol. LXIX, 1906, p 97. 



4. JORDAN, Pop. Sci. Mo., Vol. LXIX, 1906, p. 289. 



5. RANSOME, Nat. Geog. Mag., Vol. XVII, 1906, pp. 280 and 325. 



